The present disclosure relates to editing audio signals.
Audio signals are associated with a number of different parameters. An audio signal has a level value based on energy contained in the audio signal. The level value is often referred to as a root-mean-square (RMS) value. The audio signal also has a peak value and a crest factor. The peak value represents the maximum amplitude value for the audio signal within a specified time (for example, one period of an audio waveform in the audio signal). The crest factor is calculated as the ratio of the peak value and the RMS value of the audio signal over a specified time.
Editing audio signals can be accomplished using signal processing techniques to generate particular audio effects. For example, the audio signal can be adjusted to increase across time (e.g., by increasing the overall intensity of the audio signal), also referred to as amplification or applying a gain to the audio signal.
Signal intensity can vary over time such that some points in time have a high signal intensity while other points in time have a low signal intensity. Additionally, one or more factors can affect audibility of the audio signal, including, for example, background noise, number of distinct audio signal sources, or individual signal intensities. An example of audio signals having different signal intensities is a movie. The voices of different actors located at different distances from a microphone result in differences in a number of aspects including tonality, intensity, or dynamics.
In general, dynamic range is the ratio between the smallest and largest possible values of a changeable parameter. In an audio signal, dynamic range represents the ratio of the loudest portion of the audio signal to the quietest portion of the signal. Sound effects in a movie can have high signal intensities, for example explosions or water rushing from a waterfall, which affect the audio properties of dialogue. Similarly, a movie can change tempo and volume accordingly, having its characters whisper through a scene after a loud action sequence, and vice versa. Conference calls can also present challenges, with distances from the microphone and unexpected distractions, e.g., other phone calls, office machines running, and emergency service vehicles traveling nearby. Commercials (e.g., radio or television) often have a higher level than the surrounding content causing a listener to reach for her volume control after she has set the volume for the content. Other factors may also exist that influence the recording of audio signals.